/*
 * Copyright (c) 2007 innoSysTec (R) GmbH, Germany. All rights reserved.
 * Original author: Edmund Wagner
 * Creation date: 29.05.2007
 *
 * Source: $HeadURL$
 * Last changed: $LastChangedDate$
 *  
 * the unrar licence applies to all junrar source and binary distributions 
 * you are not allowed to use this source to re-create the RAR compression algorithm
 * 
 * Here some html entities which can be used for escaping javadoc tags:
 * "&":  "&#038;" or "&amp;"
 * "<":  "&#060;" or "&lt;"
 * ">":  "&#062;" or "&gt;"
 * "@":  "&#064;" 
 */
package com.github.junrar.crc;

/**
 * DOCUMENT ME
 * 
 * @author $LastChangedBy$
 * @version $LastChangedRevision$
 */
public class RarCRC {

	private final static int crcTab[];
	static {
		crcTab = new int[256];
		for (int i = 0; i < 256; i++) {
			int c = i;
			for (int j = 0; j < 8; j++) {
				if ((c & 1) != 0) {
					c >>>= 1;
					c ^= 0xEDB88320;
				} else {
					c >>>= 1;
				}
			}
			crcTab[i] = c;
		}
	}

	private RarCRC() {
	}

	public static int checkCrc(int startCrc, byte[] data, int offset, int count) {
		int size = Math.min(data.length - offset, count);
		// #if defined(LITTLE_ENDIAN) && defined(PRESENT_INT32) &&
		// defined(ALLOW_NOT_ALIGNED_INT)
		/*
		 * for (int i = 0; (0 < size) && i < data.length - 8 && ((data[i + 8] &
		 * 7) != 0); i++) { startCrc = crcTab[(short) (startCrc ^ data[i]) &
		 * 0x00FF] ^ (startCrc >>> 8); size--; }
		 * 
		 * for (int i = 0; size >= 8; i += 8) { startCrc ^= data[i + 0] << 24;
		 * startCrc ^= data[i + 1] << 16; startCrc ^= data[i + 2] << 8; startCrc
		 * ^= data[i + 3];
		 * 
		 * startCrc = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8);
		 * startCrc = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8);
		 * startCrc = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8);
		 * startCrc = crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8);
		 * 
		 * startCrc ^= data[i + 4] << 24; startCrc ^= data[i + 5] << 16;
		 * startCrc ^= data[i + 6] << 8; startCrc ^= data[i + 7]; startCrc =
		 * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc =
		 * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc =
		 * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); startCrc =
		 * crcTab[(short) startCrc & 0x00FF] ^ (startCrc >>> 8); size -= 8; }
		 */

		for (int i = 0; i < size; i++) {
			/*
			 * // (byte)(StartCRC^Data[I]) int pos = 0; // pos=0x00000000 pos |=
			 * startCrc; // pos=ffffffff
			 * 
			 * pos ^= data[i]; // data[0]=0x73=115dec --> pos=140
			 * System.out.println(Integer.toHexString(pos));
			 * 
			 * // Only last 8 bit because CRCtab has length 256 pos = pos &
			 * 0x000000FF; System.out.println("pos:"+pos); //startCrc >>>= 8;
			 * 
			 * 
			 * //StartCRC>>8 int temp =0; temp|=startCrc; temp >>>= 8;
			 * System.out.println("temp:"+Integer.toHexString(temp));
			 * 
			 * 
			 * startCrc = (crcTab[pos]^temp);
			 * System.out.println("--"+Integer.toHexString(startCrc));
			 */

			startCrc = (crcTab[(startCrc ^ data[offset + i]) & 0xff] ^ (startCrc >>> 8));

			// System.out.println(Integer.toHexString(startCrc));

			// Original code:
			// StartCRC=CRCTab[(byte)(StartCRC^Data[I])]^(StartCRC>>8);
		}
		return (startCrc);
	}

	public static short checkOldCrc(short startCrc, byte[] data, int count) {
		int n = Math.min(data.length, count);
		for (int i = 0; i < n; i++) {
			startCrc = (short) ((short) (startCrc + (short) (data[i] & 0x00ff)) & -1);
			startCrc = (short) (((startCrc << 1) | (startCrc >>> 15)) & -1);
		}
		return (startCrc);
	}

	// public static void main(String[] args)
	// {
	// RarCRC rc = new RarCRC();
	// //byte[] data = { 0x72, 0x21, 0x1A, 0x07, 0x00};
	//
	// byte[] data = {0x73 ,0x00 ,0x00 ,0x0D ,0x00 ,0x00 ,0x00 ,0x00 ,0x00 ,0x00
	// ,0x00};
	//
	// int crc = 0x90CF;
	//
	//
	// int result = rc.checkCrc(0xFFFFffff, data,0,data.length);
	// System.out.println("3: "+Integer.toHexString(~result&0xffff));
	//
	// }

}
